Revision hip surgery poses many challenges for the orthopedic surgeon and is sometimes associated with poorer long term outcomes for the patient than primary surgery. One such challenge is related to the loss of bone that results from the erosion of bone that is caused by a loosened primary implant and/or the process of removing the initial implant.
As is the case for primary surgery, the durability of implant fixation relies on the ability of the host bone to support the prosthesis over the longer term. In revision surgery, the host bone may be compromised and it is incumbent upon the surgeon to recreate a supportive bed for the revision prosthesis. Common techniques that are used to achieve this include bone grafting (autograft and allograft), the use of custom designed prosthesis that intend to fill the space once occupied by host bone and by adding shaped implant augments to a standard implant such as, for example, an acetabular cup.
Each of these techniques have limitations and problems. Autograft bone is in limited supply and often difficult to harvest creating comorbidities for the patient. Allograft bone is expensive and may or may not incorporate with the host and poses the potential for an immune response by the patient. On the other hand, custom prostheses are expensive, inexact, owing to limitations with pre-operative imaging and design. Custom prosthesis replace natural tissue with bulky, stiff implant materials that shield the host bone from stress necessary to maintain bone mineral density for the long term. Augments, like custom prosthesis, may not fit precisely and present additional bulk that can irritate soft tissue and are challenged with having adequate host bone support themselves. Surgical placement of these relatively bulky implants is often complicated and requires extensive undesirable patient exposure.
Implants of this type for the acetabulum are shown in U.S. Pat. Nos. 5,314,490; 5,702,477; 5,871,548; 6,306,173; and 7,713,306. The supplemental support structure shown in U.S. Pat. No. 5,702,447, for example, has segments extending outside the acetabulum for attachment to pelvic bone. Fixation is difficult to achieve and this rather bulky implant invades soft tissue space.